JP2014094882A - Packaging of polycrystalline silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of packaging polycrystalline silicon automatically which suppresses the produced fine powder fraction at a quite low level.SOLUTION: A method of packaging polycrystalline silicon in the form of a crushed material includes the steps of: preparing polycrystalline silicon in a measurement system; and charging the polycrystalline silicon from the measurement system removing fine powder by screening means into a plastic bag arranged under the measurement system. The weight of the introduced plastic bag charged with the polycrystalline silicon is measured in the charging operation, and the charging operation is closed after a target weight is acquired. The falling height of the polycrystalline silicon from the measurement system to the plastic bag is kept smaller than 450 mm throughout the charging operation by means of one or more clamp devices.

Description

  The present invention relates to packaging of polycrystalline silicon.

  Polycrystalline silicon (hereinafter referred to as polysilicon) is used as a starting material for the manufacture of electronic components and solar cells, among others.

  Polysilicon is obtained by thermal decomposition of a silicon-containing gas or a silicon-containing gas mixture. This operation is called deposition from the gas phase (CVD, chemical vapor deposition).

  This operation is performed on a large scale in what is called a Siemens reactor. In this case, the polysilicon is obtained in the form of rods. Polysilicon rods are generally pulverized manually.

  Numerous mechanical methods are known in which the crude pre-ground crushed polysilicon crushed material is further crushed using a conventional crusher. The mechanical grinding method is described in, for example, US Pat.

  U.S. Pat.No. 8,074,905 is an apparatus comprising a device for supplying crude polysilicon fragments in a grinding system, a grinding system, and a fractionation system for classifying polysilicon fragments, the grinding system comprising: Disclosed is an apparatus comprising a control device capable of variably adjusting at least one grinding parameter in the grinding system and / or at least one sorting parameter in the sorting system.

  In order to be used for applications in the semiconductor industry and the solar cell industry, a crushed polysilicon with as little contamination as possible is desirable. Various purification methods have also been used to achieve this.

  In US Patent Application Publication No. 2010 / 0001106A1, polysilicon obtained by the Siemens method is pulverized and classified by an apparatus equipped with a pulverizing tool and a screening device, and the polysilicon crushed material thus obtained is washed. A method for producing a high-purity classified polysilicon crushed material by washing with a chemical bath, wherein all of the pulverizing tool and the screening device have a surface in contact with the polysilicon, and the surface is A method is described in which the foreign particles are made of a material that contaminates the polysilicon crushed material, and the foreign particles are selectively removed by a subsequent cleaning bath.

  Silicon dust adhering to the crushed material is also regarded as a contaminant because it reduces the crystal pulling yield.

  US 2010/0052297 A1 discloses a method for producing polycrystalline silicon, in which polycrystalline silicon deposited on a thin rod in a Siemens reactor is crushed into crushed pieces, and the crushed pieces are about 0.5 mm to Disclosed is a method in which the crushed material is treated with compressed air or dry ice to remove silicon dust from the crushed material and is not subjected to chemical wet cleaning.

  However, the polycrystalline silicon must be packaged after the grinding process and cleaning or dedusting performed prior to shipping to the customer.

  Therefore, packaging should be performed with a minimum level of contamination.

  Typically, crushed polysilicon for the electronics industry is packaged in a 5 kg bag with a weight tolerance of +/− up to 50 g. For the solar cell industry, polysilicon shreds are usually packaged in bags with a net weight of 10 kg and a weight tolerance of +/− up to 100 g.

  Tubular bag machines are commercially available which are in principle suitable for the packaging of crushed silicon, and such packaging machines are described, for example, in DE 3640520 A1.

  However, the polysilicon crushed material is a bulk material that does not have sharp-edged fluidity, and each silicon crushed material has a weight of up to 2500 g. For this reason, care must be taken during packaging so that the material does not break through normal plastic bags during filling or in the worst case.

  To prevent these problems from occurring, commercial packaging machines must be modified to meet the purpose of polysilicon packaging.

  US Pat. No. 7,013,620B2 discloses a device for transporting, weighing, distributing, filling and packaging high-purity polysilicon crushed material at a low cost in a fully automatic manner, including a conveying groove and a hopper for crushed polysilicon material Filling to form plastic bags from high-purity plastic film, equipped with a weighing device for crushing polysilicon, a silicon turning plate, electrostatic charging of the plastic film and a deionization device thereby preventing particle contamination Flow box for preventing particle contamination of polysilicon crushed material, installed on the apparatus, welding device for plastic bags filled with crushed polysilicon, the conveying path, weighing device, filling device, and welding device Conveyor with magnetic induction detector for plastic bags filled and welded with crushed polysilicon Becomes a belt apparatus in which all of the members in contact with the polysilicon crushed are covered by or high wear resistant plastic, covered with silicon is disclosed.

  DE 10346881 A1 describes a device for filling and sealing an open plastic bag, which can be driven to rotate about a vertical axis, and filled plastic A filling machine to which a plurality of filling devices capable of suspending the bag are attached, the filling device having a welding device for making a closed seam after removing the filled plastic bag from the filling device And the apparatus also comprises a linear discharge belt for transporting the filled plastic bag from the filling machine, the rotor of the filling machine can be driven at a constant speed, and a filling stub ( a closed seam welding device assigned to the stub), and the individual welding devices on the rotor of the filling machine can rotate. A bag support is also designated, and immediately after the closure seam is created by the welding device, the plastic bag can be removed from the filling device, and the bags are fed onto a discharge belt, A system is disclosed that is driven at the circumferential speed of the rotor, is stationary with respect to the rotor, and is arranged tangentially.

  In such devices, it has been found that silicon crushing often occurs in the filling device. This catch is a drawback because it increases the time the machine is shut down.

  Plastic bag penetration also occurs, which likewise causes equipment shutdown and silicon contamination.

  It has also been found that undesirably small silicon particles or crushed materials are produced when packaging crushed materials of specific size sections, for example 20-60 mm crushed materials. The ratio of such undesired particles to such crushed material size is 17000-23000 ppmw.

  Hereinafter, all crushed pieces or particles of silicon that can be removed by a mesh screen having a square mesh of 8 mm × 8 mm are referred to as fine powder. Fine powder is undesirable for the customer because it adversely affects the operation of the customer. Even if the fines are removed by the customer, for example by screening, this adds cost and inconvenience.

  For example, similar to the automatic packaging of polycrystalline silicon according to US Pat. No. 7,013,620 B2, manual packaging of polycrystalline silicon in a plastic bag is an option. Manual packaging can clearly reduce the fines fraction, reducing to 1400 ppmw to 17000 ppmw for the 20-60 mm crushed size described above.

  However, manual packaging is very inconvenient and leads to increased labor costs. Therefore, manual packaging is not an option for economic reasons. Furthermore, it is desired to reduce the fine powder fraction further than the fine powder fraction achieved by manual packaging.

U.S. Pat. No. 8021483B2 US Patent No. 8074905 US Patent Application Publication No. 2010 / 0001106A1 US Patent Application Publication No. 2010 / 0052297A1 German Patent Application Publication No. 3640520A1 US Pat. No. 7,013,620B2 German Patent Application No. 103466881A1

  The object of the present invention is therefore to automatically package polycrystalline silicon and to keep the resulting fines fraction to a very low level. The present invention also provides an apparatus suitable for this purpose.

The purpose of the present invention is to
-Preparing polycrystalline silicon in a metering system;
Filling the polycrystalline silicon from the weighing system that removes fines by screening means into a plastic bag located under the weighing system, the method comprising:
The weight of the plastic bag containing the introduced polycrystalline silicon is measured during the filling operation, and after the target weight is obtained, the filling operation is terminated.
This is achieved by a method in which the drop height of the polycrystalline silicon from the weighing system into the plastic bag is maintained below 450 mm for the full filling operation by means of at least one clamping device.

  Preferably, the drop height of the polycrystalline silicon from the weighing system into the plastic bag is maintained below 300 mm for the full filling operation by at least one clamping device.

  The above object is a clamping device for an apparatus for packaging polycrystalline silicon in a plastic bag, which acts on the plastic bag to be pressed horizontally by a clamp at a specific point, wherein the plastic bag This is achieved by a device in which the cross-sectional area of the plastic bag is reduced and the clamp can be released completely or partially at any point, and the cross-sectional area of the plastic bag increases again at this point.

  Also, the above object is a method of packaging polycrystalline silicon by filling the plastic bag with polycrystalline silicon, which acts on the plastic bag to be pressed horizontally by a clamp at a specific point By using at least one clamping device, the cross-sectional area of the plastic bag is reduced and the vertically introduced polycrystalline silicon can reach the plastic bag up to this point, completely or partially at any point in time. Achieved by a method in which the clamp can be released and the cross-sectional area of the plastic bag increases again at this point and the polycrystalline silicon can move further down into the plastic bag perpendicularly from this point. Is done.

  It has been found that the new fines fraction produced during packaging is much less than with conventional automatic packaging methods. For example, the fine powder fraction for a crushed material size of 20 to 60 mm is 1400 ppmw or less.

  The present invention starts from a crushed silicon sized to a specific size obtained by grinding rods deposited by the Siemens method, followed by fractionation and classification.

The size classification is determined as the longest distance (= maximum length) between two points on the surface of the silicon fragment.
Crushed material size 0 [mm] 1-5
Crushed material size 1 [mm] 4-15
Crushed material size 2 [mm] 10-40

Similar to the above size classification, the classification and fractionation of polycrystalline silicon into the following crushed material sizes are performed in the same manner.
Crushed material size 3 [mm] 20-60
Crushed material size 4 [mm] 45-120
Crushed material size 5 [mm] 90-200

  Under this circumstance, in each case, at least 90% by weight of the crushed fraction is within the specified size range.

  The polysilicon crushed material is conveyed by a conveyance groove (conveyance path), and separated into a coarse crushed material and a fine crushed material by at least one sieve.

  The method according to the invention, unlike the prior art, in which the crushed material is weighed with a weighing balance, weighed to the target weight, then separated by a removal groove (removal channel), transported to a packaging unit and packaged. Now, weigh and package in one step.

  The metering system is designed so that fines, ie ultrafine particles and debris of polysilicon, are removed by a sieve before the filling operation. The sieve may be a perforated plate, a rod-shaped (rod-shaped) sieve, a photopneumatic fractionation device or other suitable device. Different sieves can be used depending on the size of the crushed material. It is preferable to use a sieve having a sieve width of 3 mm for the size of a crushed material of 20 to 60 mm. It is preferable to use a sieve having a sieve width of 9 mm for the size of the crushed material of 45 to 120 mm.

  Preferably, the surface of the sieve used comprises at least part of a low-contamination material such as, for example, a hard metal. Hard metal shall mean sintered carbide hard metal. In addition to conventional hard metals based on tungsten carbide, there are also hard metals, preferably including titanium carbide and titanium nitride, as hard materials, in which case the binder phase comprises nickel, cobalt and molybdenum. Become.

  Preferably, the at least mechanically stressed, wear-sensitive surface area of the sieve comprises hard metal or ceramic / carbide. Preferably, at least one sieve is made entirely from hard metal. The sieve can be coated partially or over the entire surface. The coating used is preferably a material selected from the group consisting of titanium nitride, titanium carbide, titanium aluminum nitride, and DLC (diamond-like carbon).

  The polysilicon crushed material is introduced into the plastic bag by the weighing unit, which preferably has a transport path suitable for conveying the product stream of crushed material, the product stream, the coarse crushed material, and the fine crushed material. It comprises at least one sieve suitable for separating the product, a coarse measuring groove (coarse measuring channel) for coarsely crushed material, and a fine measuring groove (fine measuring channel) for fine crushed material.

  By separating the product stream into coarse crushed material and fine crushed material, more accurate metering of polysilicon is possible.

  The size distribution of the polysilicon fragment in the starting material stream depends on factors that include the preceding grinding operation. The method of splitting into coarse and fine crushed pieces and the size of the coarse and fine crushed pieces will depend on the desired end product to be weighed and packaged.

  A typical size distribution of crushed material comprises crushed material having a size of 1 to 200 mm.

  For example, crushed material having a size smaller than a specific size can be carried out from the weighing unit using a sieve connected to the carry-out groove, preferably using a rod-like sieve. Thereby, only crushed material of a very specific size classification can be weighed and packaged.

  Due to the transfer of polysilicon in the transfer groove (transfer path), a new undesirable product size is generated. These product sizes are removed with a sieve by a sieve.

  The removed small debris is again classified, weighed and packaged in downstream operations or sent to other applications.

  The metering of polysilicon through two metering paths can be automated.

  The silicon product stream can be divided into a plurality of integrated metering and packaging systems by a tuned rotating path.

  Preferably, together with the packaging and gripping system, the polycrystalline silicon is filled directly from the weighing system into a plastic bag, in particular a PE bag, and weighed. The weighing system is based on a total weight balance system.

  The clamping device is used to compress the bag during the filling operation. This prevents the polycrystalline silicon from falling through the entire length of the bag. The clamping device acts as a kind of fall arrestor and squeezes the plastic bag so that the cross-sectional area of the plastic bag is initially reduced and then released under control.

  This makes it possible to control the product flow, producing only a small fraction of fines and filling the prefabricated bag with silicon.

  The fine powder is preferably removed by a measuring groove fitted with a removal mechanism, particularly a rod-shaped sieve for removing fine powder, at the end.

  Preferably, at least one clamping device opens when a specific filling height and a specific weight of polycrystalline silicon are reached in the bag.

  According to the invention, the product stream can be guided into the bag without fines. This is achieved by low contamination sieving in the metering system. The adjusted placement of the metering channel (additional fine metering channel) allows the product stream to be fitted very close to the opened bag. Thus, the material flow can be filled into the bag with an absolute minimum drop height. Preferably, the filling is performed via a bayonet funnel. The bayonet funnel is preferably made of a material with low levels of silicon contamination.

  With a suitable sensor, a further drop in drop height is recorded during the filling operation.

  When the drop height reaches near 0 mm, immediately release the product clamp so that the material falls to the bottom of the next clamp or bag.

  Preferably, the damping and storage element is swirled in the product stream. These elements are preferably made of a low contamination material and coated with a low contamination material. These elements achieve a certain damping effect on the product stream and absorb energy, and these elements are filled with polycrystalline silicon. After the plastic bag is partially filled, these elements are emptied and removed again from the product stream. This is preferred in order to achieve first the cycle speed and secondly to further reduce the drop height.

  Preferably, the polysilicon crushed material is recorded by a camera before the weighing operation, and the specific gravity of the crushed material is measured during this process, and the surface characteristics of the crushed material are recognized.

  This enables a packaging operation that protects the bag more accurately.

Claims (10)

-Preparing polycrystalline silicon in the weighing system;
Filling the polycrystalline silicon from the weighing system, which removes fines by screening means, into a plastic bag arranged under the weighing system; A method,
The weight of the plastic bag containing the introduced polycrystalline silicon is measured during the filling operation, and after the target weight is obtained, the filling operation is terminated.
A method wherein the drop height of the polycrystalline silicon from the weighing system into the plastic bag is maintained below 450 mm for the full filling operation by at least one clamping device.   The method of claim 1, wherein the metering system comprises a coarse metering groove for coarse crushed material and a fine metering groove for fine crushed material.   The clamping device is designed such that the plastic bag is squeezed during the filling operation so that the cross-sectional area of the plastic bag is initially reduced and then released under control. Or the method of 2.   4. A method according to claim 3, wherein several clamping devices of this kind are equipped over the entire length of the plastic bag, and these clamping devices are gradually released as the filling of the plastic bag increases.   The method according to claim 1, wherein the polycrystalline silicon is filled into the plastic bag via a bayonet funnel.   The dampening and storage element is swiveled in a polysilicon stream between a metering system and a plastic bag, filled with debris, emptied and removed again after a specified filling level of the plastic bag. The method as described in any one of -5.   The method according to claim 1, wherein before the weighing, the polycrystalline silicon is recorded using a camera to determine the specific gravity and surface characteristics of the polycrystalline silicon.   The drop height of the polycrystalline silicon from the weighing system into the plastic bag is maintained at less than 300 mm for the full filling operation by at least one clamping device. the method of. A clamping device for a device for packaging polycrystalline silicon in a plastic bag,
Acts on the plastic bag to compress horizontally by a clamp at a certain point, the cross-sectional area of the plastic bag is reduced, and the clamp can be fully or partially released at any point, Clamping device, wherein the cross-sectional area of the plastic bag increases again at this point. A method of packaging polycrystalline silicon by filling in a plastic bag,
By using at least one clamping device acting on the plastic bag and pressing horizontally with a clamp at a specific point, the cross-sectional area of the plastic bag is reduced and the vertically introduced polycrystalline silicon is this The plastic bag can be reached up to a point, and at any point the clamp can be fully or partially released, the cross-sectional area of the plastic bag increases again at this point, and the polycrystalline silicon A method which can be moved further down into the plastic bag in a vertical direction from a point.